Display unit and method of manufacturing the same

ABSTRACT

A display unit includes, on an insulating substrate, a plurality of wirings formed to extend in different directions, a thin-film transistor, and a display element. At least one of the plurality of wirings is a divided wiring having a crossing portion formed at an intersection with the other of the plurality of wirings, and a main portion which is formed in a layer same as the other of the plurality of wirings with an insulating film in between and which is electrically connected to the crossing portion via an conductive connection provided in the insulating film. At least one of the main portion and the crossing portion includes a first layer and a second layer stacked in order from the insulating substrate side, the second layer being in direct contact with the first layer and made of a material of a higher melting point than the first layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP2007-272754 filed in the Japanese Patent Office on Oct.19, 2007, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display unit which is suitablyapplied to an organic electro luminescence display or liquid crystaldisplay for example, and also relates to a method of manufacturing thesame.

2. Description of the Related Art

In recent years, development of next-generation displays is active dueto an increasing demand for space-saving, high luminance, low powerconsumption and so on. In such situation, the organic electroluminescence display (organic EL display) using an organic lightemitting element attracts attention as those satisfying such demands. Inthe organic electro luminescence display, wide viewing angle isavailable due to its light-emitting feature. What is more, since nobacklight is necessary, it is possible to realize power saving and highresponsiveness and further to reduce thickness in dimension. Inaddition, the organic electro luminescence display attracts moreattention due to its flexibility when using a plastic plate as asubstrate to utilize the flexible nature inherent to organic luminescentmaterials.

As for a drive system of the organic electro luminescence display, theactive matrix system, in which a thin film transistor (TFT) is used asits drive element, recognizes advantages in response time and resolutioncompared with the passive matrix system of related art, therebyconsidered to be much suitable for the organic electro luminescencedisplay having features as mentioned above.

As for the thin film transistor used in the active matrix organicelectro luminescence display, at least a switching transistor forcontrolling the tone of a pixel and a drive transistor for controllinglight emission of the organic light emitting element are necessary. Acapacitor is connected to a gate electrode of the drive transistor tohold an electric charge in accordance with a display signal.

Due to its enlarged display size and advanced fineness, such activematrix organic light emitting element suffers from disadvantages oflonger and finer gate wiring, source signal line and current supplyline. However, the resistance of wiring increases in proportion to thelength and in inverse proportion to the cross-section area. Suchincrease in resistance results in a distortion of signal waveform andtransmission delay of signals, thereby leading to unevenness anddegradation of image quality.

In order to lower the wiring resistance, usage of a low resistancematerial such as aluminum (Al) may be useful. However, such lowresistance material as aluminum (Al) does not have enough thermalresistance. Since it is inevitable in the manufacturing process of athin film transistor, which includes a gate insulating film for example,to raise the temperature of a substrate to 300° C. or more, independentusage of aluminum (Al) may cause a hillock due to the thermal stress,thereby deterioration of insulation quality is observed in interlayerinsulating films.

For example, disclosure by Japanese Patent Publication No. 2003-45966shows that a scanning line 3 a and a main portion 61 a of a data line 6a are made of a low resistance metal such as aluminum or an aluminumalloy. Here, at the wiring intersection, a relay portion 62 a of thedata line 6 a, which is made of a refractory metal, is disposed underthe scanning line 3 a and a capacitance line 3 b. Such divided wiringenables to suppress the generation of hillock at the intersection evenwhen the relay portion is exposed to high temperature in themanufacturing process of a thin film transistor.

SUMMARY OF THE INVENTION

However, in the above-mentioned disclosure, since the relay portion 62 ais not made of a low resistance metal, wiring resistance increases morethan a little so that there is a possibility of signal transmissiondelay for a larger screen.

Incidentally, disclosure by Japanese Patent Publication No. 07-86230shows that after oxidizing the surface of an aluminum (Al) wiring underan oxygen atmosphere, it is covered with a high-melting material. Inthis case, the oxide film formed between the aluminum (Al) wiring andthe high-melting material has a resistance component characteristic. Inthe case of normal wiring other than the divided wiring, since thealuminum (Al) wiring and the high-melting material are connected atseveral points through a pinhole or the like, the resistance componentdoes not become an issue. However, when the disclosure is applied to theabove-mentioned divided wiring, there appears the resistance componentin each relay portion, thereby the low resistance feature of the lowerlayer is scarcely used efficiently as if it were solely configured bythe upper refractory metal. As a result, it is difficult to sufficientlyreduce the wiring resistance, which results in a distortion of signalwaveform and transmission delay of signals, thereby leading tounevenness and degradation of image quality.

In the manufacturing process of a thin film transistor, sometimes laserirradiation is applied to the whole surface of a substrate for thepurpose of silicon crystallization. In that case, low resistancematerials such as aluminum (Al) may not be used even when it is coveredwith a refractory metal because there may be a shortcoming of thermalresistance or diffusion in high temperatures.

In view of the above-mentioned drawbacks, it is desirable to provide adisplay capable of reducing the wiring resistance of a divided wiring toimprove the image quality, and a method of manufacturing the same.

According to an embodiment of the present invention, there is provided adisplay unit including, on an insulating substrate, a plurality ofwirings formed to extend in different directions, a thin-film transistorand a display element. Among the plurality of wirings, at least one ofthem is a divided wiring having a crossing portion formed at anintersection with the other of the plurality of wirings and a mainportion which is formed in a layer same as the other of the plurality ofwirings with an insulating film in between and which is electricallyconnected to the crossing portion via an conductive connection providedin the insulating film. Among the main portion and the crossing portion,at least one of them includes a first layer and a second layer stackedin order from the insulating substrate side. The second layer is indirect contact with the first layer and made of a material of a highermelting point than the first layer.

According to an embodiment of the present invention, there is provided amethod of manufacturing a display unit which is constituted from stepsof forming, on an insulating substrate, a plurality of wirings includinga source signal line and a gate wiring, a thin film transistor and adisplay element. The step of forming the plurality of wiring includesthe steps of forming a crossing portion of the source signal line at anintersection with the gate wiring, forming an insulating film on theinsulating substrate on which the crossing portion is formed, andforming a main portion of the source signal line and the gate wiring onthe insulating film and providing a conductive connection in theinsulating film for electrically connecting the main portion and thecrossing portion. In the step of forming the crossing portion of thesource signal line, a first layer and a second layer made of a materialof a higher melting point than the first layer are continuously formedin order from the insulating substrate side.

In the display unit of the embodiment of the present invention, sincethe first layer and the second layer made of a material of a highermelting point than the first layer are in direct contact with eachother, the resistance of the crossing portion is reduced. This allowsthe divided wiring to reduce its wiring resistance, thereby suppressinga distortion of signal waveform and transmission delay of signals, etc.,so as to improve the image quality.

According to a display unit of the embodiment of the present invention,since a first layer and a second layer made of a material of a highermelting point than the first layer are in direct contact with eachother, the resistance of a crossing portion is lowered. This allows adivided wiring to reduce wiring resistance, thereby suppressing adistortion of signal waveform and transmission delay of signals, etc.,to improve the image quality. According to a method of manufacturing adisplay unit of the embodiment of the present invention, since the firstlayer and the second layer are formed continuously, formation of thedisplay unit of the embodiment of the present invention becomes easier.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a display unit according to a firstembodiment of the present invention.

FIG. 2 is a representative circuit schematic showing an example of apixel driving circuit appearing in FIG. 1.

FIG. 3 is a sectional view showing an example of a drive transistor anda write transistor appearing in FIG. 2.

FIG. 4 is a plan view showing an example of the pixel driving circuitappearing in FIG. 2.

FIG. 5 is a perspective view showing the configuration of a gate wiring,current supply line and a source signal line at the intersectionthereof.

FIG. 6 is a sectional view showing the configuration of a crossingportion appearing in FIG. 5.

FIG. 7 is a sectional view showing the configuration of the display unitof FIG. 1.

FIGS. 8A and 8B are sectional views showing step of manufacturing thedisplay unit of FIG. 1 in the processing sequence.

FIG. 9 is plan view of a step subsequent to FIGS. 8A and 8B.

FIG. 10 is a sectional view showing the configuration of a crossingportion of a source signal line provided in a display unit according toa second embodiment of the present invention.

FIG. 11 is a sectional view showing the configuration of a display unitaccording to a third embodiment of the present invention.

FIG. 12 is a plan view showing the schematic constitution of a modulewhich includes the display unit according to the first to thirdembodiments.

FIG. 13 is a perspective view showing an external appearance ofapplication example 1, to which the display unit of the first to thirdembodiments is applied.

FIG. 14A is a perspective view showing an external appearance ofapplication example 2 as seen from the front side, and FIG

FIG. 14B is a perspective view thereof as seen from the backside.

FIG. 15 is a perspective view showing an external appearance ofapplication example 3.

FIG. 16 is a perspective view showing an external appearance ofapplication example 4.

FIG. 17A is a front elevation view of application example 5 when it isopened,

FIG. 17B is a side elevation view thereof,

FIG. 17C is a front elevation view of the application example 5 when itis closed,

FIG. 17D is a left side view thereof,

FIG. 17E is a right side view and

FIG. 17F is a top view thereof, and

FIG. 17G is a bottom view thereof.

FIG. 18 is a perspective view showing the configuration of a gatewiring, current supply line and a source signal line at the intersectionthereof according to comparative example 2.

FIG. 19 is a graph showing a cumulative failure rate computed for eachof the examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detailhereinbelow with reference to the drawings.

First Embodiment

FIG. 1 shows a configuration of display unit according to a firstembodiment of the present invention. The display unit is used as anultrathin color organic EL display and so on, and is typicallyconfigured in such a manner that a display region 110, which isconstituted from an after-mentioned plurality of organic light emittingelements 10R, 10G and 10B arrayed in matrix, is disposed on aninsulating substrate 11 made of a glass or a plastic, while a signalline driving circuit 120 and a scanning line driving circuit 130, whichare drivers for video display, are formed around the display region 110.

A pixel driving circuit 140 is formed in the display region 110. Aplurality of gate wirings X1 are arranged in rows and a plurality ofsource signal lines Y1 are arranged in columns on the pixel drivingcircuit 140. Each intersection between the respective gate wirings X1and the source signal lines Y1 corresponds to any one of the organiclight emitting elements 10R, 10G, and 10B (subpixels) one to one. Eachof the source signal lines Y1 is connected to the signal line drivingcircuit 120 so that an image signal is supplied from the signal linedriving circuit 120 to an after-mentioned source electrode of a writetransistor Tr2 via the source signal lines Y1. Each of the gate wiringsX1 is connected to the scanning line driving circuit 130 so that a scansignal is sequentially supplied from the scanning line driving circuit130 to a gate electrode of the write transistor Tr2 via the gate wiringsX1.

FIG. 2 is an example of the pixel driving circuit 140. The pixel drivingcircuit 140, which is formed in a lower layer of an after-mentionedfirst electrode 13, is an active driving circuit including a drivetransistor Tr1, the write transistor Tr2, a capacitor Cs, and theorganic light emitting element 10R (or 10G, 10B).

The gate electrode of the write transistor Tr2 is connected to the gatewiring X1, the source electrode thereof is connected to the sourcesignal line Y1, and the drain electrode thereof is connected to the gateelectrode of the drive transistor Tr1 and one end of the capacitor Cs.The source electrode of the drive transistor Tr1 is connected to acurrent supply line Y2 which extends in a lengthwise direction and thedrain electrode thereof is connected to the organic light emittingelement 10R (or 10G, 10B). The other end of the capacitor Cs isconnected to the current supply line Y2.

FIG. 3 shows an example of the drive transistor Tr1 and the writetransistor Tr2. The drive transistor Tr1 and the write transistor Tr2are typically thin film transistors of an inverse-stagger structure(what is called bottom gate TFT), in which a gate electrode 151, a gateinsulating film 152, a semiconductor film 153, an etching stop layer154, an n⁺a-Si layer 155, and source/drain electrode 156 are disposed inorder on the insulating substrate 11, and finally the passivation film157 is formed to cover the whole surface. It is to be noted thatconfigurations of the drive transistor Tr1 and the write transistor Tr2are not limited to the above in particular and may be of a staggerstructure (top gate TFT).

The gate electrode 151 is made of a metal or an alloy containing atleast one sort of refractory metals selected from the group consistingof molybdenum (Mo), chromium (Cr), titanium (Ti), tungsten (W) andtantalum (Ta) for example.

The gate insulating film 152 is structured in such a manner that a SiNxlayer 152A (100 nm thick) and a SiOx layer 152B (200 nm thick) arestacked in order from the gate electrode 151 side, for example.Preferably, the thickness of the gate insulating film 152 is within arange of the order of 50 nm to 700 nm in total in consideration of thebalance of leakage current and capacity.

The semiconductor film 153, which is typically formed to the thicknessof 10 nm to 50 nm, is formed by annealing, in which an a-Si film isirradiated with a laser beam to obtain a polycrystalline silicon (p-Si)or a microcrystal silicon. This annealing process is necessary forreducing the induction of threshold shift of the drive transistor Tr1 orthe write transistor Tr2. Namely, it is known that, in the thin filmtransistor used in an organic electro luminescence display, a long-timevoltage application to the gate electrode may induce a shift ofthreshold voltage. What is worse, since the thin film transistor used inthe organic electro luminescence display needs be continuously energizedas long as the organic light emitting elements 10R, 10G, and 10B areemitting light, it is more liable to induce the threshold shift. Whenthe threshold voltage of the drive transistor Tr1 shifts, the currentamount passing through the drive transistor Tr1 is changed, thereby theluminance of the organic light emitting elements 10R, 10G, and 10Bconstituting each pixel is also changed. To reduce threshold shift forthe drive transistor Tr1, it is useful to crystallize the semiconductorfilm 153 by annealing so that a channel region thereof may be formed ofthe polycrystalline silicon or microcrystal silicon.

The etching stop layer 154 is made of SiNx, SiOx, or SiON, and typicallyformed to the thickness of 50 nm to 500 nm, specifically, of the orderof 200 nm.

The n⁺a-Si layer 155 is typically formed to the thickness of 10 nm to300 nm, more specifically, of the order of 100 nm.

The source/drain electrode 156 has a stacked structure of an aluminum(Al) layer and a titanium (Ti) layer, for example.

FIG. 4 is a planar configuration of the pixel driving circuit 140 shownin FIG. 2, and FIG. 5 shows the intersection between the source signalline Y1 and the gate wiring X1 and the current supply line Y2 of FIG. 4.The gate wiring X1 and the current supply line Y2 are extending in thewidthwise direction. The source signal line Y1 which extends in alengthwise direction crosses perpendicular to the gate wiring X1 and thecurrent supply line Y2.

The source signal line Y1 is divided into a main portion 170 and acrossing portion 160 at the intersection with the gate wiring X1 and thecurrent supply line Y2. The crossing portion 160 is formed in a layersame as the gate electrode 151, and the main portion 170 is formed in alayer same as the source/drain electrode 156, gate wiring X1 and thecurrent supply line Y2, with the gate insulating film 152 in between.The crossing portion 160 and the main portion 170 are electricallyconnected via a conductive connection 180 provided in the gateinsulating film 152.

FIG. 6 shows a cross-sectional configuration of the crossing portion160. The crossing portion 160 includes a first layer 161 and a secondlayer 162 made of a material having a higher melting point than thefirst layer 161 in order from the insulating substrate 11 side.

The first layer 161 is made of a metal or an alloy containing at leastone sort of low resistance metal selected from the group consisting ofaluminum (Al), copper (Cu) and silver (Ag) for example. Thickness of thefirst layer 161 needs to be determined in accordance with necessaryresistance, but the thickness of the order of 50 nm to 1000 nm ispreferable from a viewpoint of thermal resistance. Configuration of thefirst layer 161 may be a single structure or a stacked structureincluding two or more layers.

The second layer 162 is made of a material having a higher melting pointthan the first layer 161. More specifically, examples of a componentmaterial constituting the second layer 162 include a metal or alloycontaining at least one selected from the group consisting of molybdenum(Mo), chromium (Cr), titanium (Ti), tungsten (W), tantalum (Ta),vanadium (V), niobium (Nb), nickel (Ni) and magnesium (Mg). Above all,what is called refractory metal or an alloy thereof, such as molybdenum(Mo), tungsten (W), tantalum (Ta), and niobium (Nb) are the mostpreferable. It may otherwise be constituted from a compound conductivematerial such as indium oxide or zinc oxide. It is necessary to adjustthe thickness of the second layer 162 so as to prevent any trouble inthe first layer 161 even when its thermal resistance is low, and it ispreferred that the thickness is of the order of 10 nm to 200 nm forexample. Configuration of the second layer 162 may be a single layer ora stacked structure including two or more layers.

Since the first layer 161 and the second layer 162 are continuouslyformed as mentioned later, they are in direct contact with each otherwithout forming a natural surface oxide film in between. This makes itpossible for the display unit to reduce a wiring resistance of thesource signal line Y1, thereby improving the image quality.

The upper surface and side face of the crossing portion 160 are coveredwith a cap layer 164. Since the cap layer 164 covers the side of thefirst layer 161 so as to prevent it from exposure, even when the thermalresistance of the first layer 161 is low, the hillock etc., caused byannealing is suppressed. As a result, the pressure resistance of thegate insulating film 152 is improved. The cap layer 164 is made of amaterial or alloy containing at least one sort of refractory metalhaving a higher melting point than the first layer 161, as typicallyselected from the group consisting of molybdenum (Mo), tungsten (W),tantalum (Ta) and niobium (Nb).

The main portion 170 has a stacked structure of aluminum (Al) layer andtitanium (Ti) layer similar to the source/drain electrode 156, forexample.

Location of the crossing portion 160 and the main portion 170 isdetermined in consideration of an irradiation area R of the laser beamLB, for annealing the semiconductor film 153 as shown in FIG. 9. Here,the crossing portion 160 is formed outside the irradiation area R of thelaser beam LB. Since irradiation with the laser beam LB is a heattreatment of 400° C. or higher, there may be a possibility of thermalresistance or diffusion in such high temperature even if the first layer161, which is typically made of a low resistance metal, is covered withthe second layer 162 which is mainly made of a refractory metal. Thus,it is preferred to form the crossing portion 160 outside the irradiationarea R of the laser beam LB so as to avoid thermal damage given by thelaser beam LB.

FIG. 7 is a cross-sectional configuration of the display region 110. Theorganic light emitting element 10R which emits a red light, the organiclight emitting element 10G which emits a green light, and the organiclight emitting element 10B which emits a blue light are sequentiallyarrayed on the display region 110 so as to form a matrix as a whole. Itis to be noted that the organic light emitting elements 10R, 10G, and10B have a planar rectangular configuration, and combination ofneighboring three organic light emitting elements 10R, 10G and 10Bconstitutes one pixel.

Each of the organic light emitting elements 10R, 10G and 10B isconfigured in such a manner that a drive transistor Tr1 provided in theabove-mentioned pixel driving circuit 140, a planarization insulatingfilm 12, a first electrode 13 as anode, an inter-electrode insulatingfilm 14, an organic layer 15 including an after-mentioned light emittinglayer, and a second electrode 16 as cathode are stacked in order fromthe substrate 11 side.

Such organic light emitting elements 10R, 10G, and 10B are covered asnecessary with a protective film 17 typically made of silicon nitride(SiN) or silicon oxide (SiO). Then, a sealing substrate 21 typicallymade of glass is further laminated over the whole surface of theprotective film 17, with an adhesive layer 30 typically made of athermosetting resin or an ultraviolet curing resin in between, for thepurpose of sealing. A color filter 22 and a light shielding film (notshown) as a black matrix may be disposed as necessary on the sealingsubstrate 21.

The drive transistor Tr1 is electrically connected to the firstelectrode 13 via a connection hole 12A provided in the planarizationinsulating film 12.

The planarization insulating film 12, which is necessary for planarizingthe face of the substrate 11 on which the pixel driving circuit 140 isformed, is preferably made of a material having a good pattern accuracyfor facilitating formation of a fine connection hole 12A. Examples ofcomponent materials of the planarization insulating film 12 includeorganic materials such as polyimide, and inorganic materials such assilicon oxide (SiO₂).

The first electrodes 13 are formed corresponding to the organic lightemitting elements 10R, 10G and 10B, respectively. Since the firstelectrode 13 has a function as a reflecting electrode to reflect a lightemitted from the light emitting layer, it is desirable to have the highpossible reflectance as much as possible so as to raise the luminousefficiency. The first electrode 13, which is typically formed to thethickness of 100 nm to 1000 nm, is made of a simple substance or alloyof such metallic element as silver (Ag), aluminum (Al), chromium (Cr),titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo),copper (Cu), tantalum (Ta), tungsten (W) platinum (Pt) and gold (Au).

The inter-electrode insulating film 14 secures insulation between thefirst electrode 13 and the second electrode 16 and accurately secures adesired shape of the light-emitting region. It is typically made of anorganic material such as polyimide, or an inorganic insulating materialsuch as silicon oxide (SiO₂). Here, openings are provided in theinter-electrode insulating film 14 corresponding to the respectivelight-emitting regions in the first electrode 13. The organic layer 15and the second electrode 16 may be extended continuously not only on thelight-emitting region but also on the inter-electrode insulating film14. Anyway, light is emitted only through the openings provided in theinter-electrode insulating film 14.

The organic layer 15 here is structured in such a manner that a holeinjection layer, a hole transport layer, a light emitting layer and anelectron transport layer (none of them are illustrated) are stacked inorder from the first electrode 13 side. However, they are not alwaysindispensable except the light emitting layer, and may be provided ifnecessary. In addition, the organic layer 15 may be configureddifferently depending on the emission color of the respective organiclight emitting elements 10R, 10G and 10B. The hole injection layerincreases the hole injection efficiency as well as works as a bufferlayer for preventing leakage current. The hole transporting layer has afunction of increasing the efficiency in transporting holes to the lightemitting layer. The light emitting layer emits light when an electricfield is applied because that induces the recombination of electrons andholes. The electron transport layer increases the efficiency intransporting electrons to the light emitting layer. The componentmaterial of the organic layer 15 may be a general low-molecular orpolymeric organic material, and is not limited in particular.

The second electrode 16, which is typically formed to the thickness of 5nm to 50 nm, is made of a simple substance or alloy of a metallicelement such as aluminum (Al), magnesium (Mg), calcium (Ca), and sodium(Na) Above all, an alloy of magnesium and silver (MgAg alloy) or analloy of aluminum (Al) and lithium (Li) (AlLi alloy) are desirable. Thesecond electrode 16 may be made of ITO (indium-tin composite oxide) orIZO (indium-zinc composite oxide).

This display unit may be manufactured in a manner as described below,for example.

FIGS. 8A, 8B and 9 are views for explaining the method of manufacturingthe display unit. The method of manufacturing the display unit typicallyincludes a step of forming the above-mentioned pixel driving circuit 140on the substrate 11, and a step of forming the organic light emittingelements 10R, 10G and 10B.

Step of Forming the Pixel Driving Circuit 140

First, as shown in FIG. 8A, the first layer 161 and second layer 162 ofthe material and thickness as mentioned above, are continuously formedon the substrate 11 of the above-mentioned material typically by asputtering method, without being exposed to the atmosphere. Then, theyare formed into a predetermined shape by photolithography and etchingfor example, so as to obtain the crossing portion 160. Since the firstand the second layers 161 and 162 are continuously formed, they are indirect contact with each other to prevent formation of natural oxidationfilm or the like having a characteristic as a resistance component. Thisallows the crossing portion 160 to reduce its resistance, therebyenabling to reduce the wiring resistance of the source signal line Y1.

Subsequently, as shown in FIG. 8B, the cap layer 164 made of theabove-mentioned material is formed typically by a sputtering method andformed into a predetermined shape typically by photolithography andetching so that the upper surface and the side face of the crossingportion 160 are covered with the cap layer 164. Simultaneously, the gateelectrode 151 is formed using the same component material as the caplayer 164. In this manner, production process is simplified.

Subsequently, the gate insulating film 152 and the semiconductor film153 of the material and thickness as mentioned above are formedtypically by plasma CVD (chemical vapor deposition).

Then, the semiconductor film 153 is irradiated with the laser beam LBfor annealing using a solid state laser oscillator so as to crystallizea-Si constituting the semiconductor film 153. At this time, as shown inFIG. 4, the laser beam LB has its lengthwise dimension a little narrowerthan that of the pixel size and scanning along the minor axial directionof pixels. Namely, since the irradiation area R of the laser beam LB isdefined by the shaded portion of FIG. 9, it is shown that the drivetransistor Tr1 and the write transistor Tr2 are formed within theirradiation area R of the laser beam LB but the crossing portion 160 isformed outside the irradiation area R. Since irradiation of the laserbeam LB is able to thus avoid the crossing portion 160, that allows thefirst layer 161 not only to prevent from being damaged due to a hightemperature heating of 400° C. or higher under laser irradiation, butalso to be processed at a high processing speed.

Otherwise, as the laser beam LB, an excimer laser beam having the sameminor-axial dimension as the pixel size may be employed so thatirradiation is applied by repetition of pixel-length step moving andpulse irradiation in the minor-axial direction.

After irradiating the semiconductor film 153 with the laser beam LB, theetching stop layer 154 of the above-mentioned thickness and material isformed on the crystallized semiconductor film 153, then it is formedinto a predetermined shape by an etching process for example so that theetching stop layer 154 may be left only on an area which will finallybecome the channel region.

After forming the etching stop layer 154, the n⁺a-Si layer 155 of theabove-mentioned thickness is formed on the etching stop layer 154 andthe crystallized semiconductor film 153 by a CVD process for example,then is formed into a predetermined shape typically by etching.

After forming the n⁺a-Si layer 155, the source/drain electrode 156 ofthe above-mentioned material is formed thereon by sputtering forexample, then it is formed into a predetermined shape typically byetching. At this time, the gate wiring X1, the current supply line Y2,and the main portion 170 of the source signal line Y1 made of theabove-mentioned materials are also formed and connected to thesource/drain electrode 156. The main portion 170 of the source signalline Y1 is connected to the crossing portion 160 via the conductiveconnection 180 provided in the gate insulating film 152. In addition,the passivation film 157 is formed to cover the whole surface. In thismanner, the pixel driving circuit 140 as shown in FIGS. 1 to 6 is thuscompleted.

Step of Forming the Organic Light Emitting Elements 10R, 10G and 10B

Subsequently, the planarization insulating film 12 is formed bytypically applying the above-mentioned material on the pixel drivingcircuit 140 by, for example a spin coat method then exposing anddeveloping it.

After that, on the planarization insulating film 12, the first electrode13 made of the above-mentioned material is formed by DC sputtering forexample, then selectively etched by lithography technology for example,to be pattered into a predetermined shape. Subsequently, theinter-electrode insulating film 14 of the above-mentioned thickness andmaterial is formed typically by CVD, then openings are formed in theinter-electrode insulating film 14 using a lithography technology forexample. After that, the organic layer 15 and the second electrode 16 ofthe above-mentioned materials are formed sequentially by an evaporationmethod for example so as to obtain the organic light emitting elements10R, 10G and 10B. Then, the protective film 17 made of theabove-mentioned material is formed so as to cover the organic lightemitting elements 10R, 10G and 10B.

Subsequently, the adhesive layer 30 is formed on the protective film 17.Then, the sealing substrate 21 made of the above-mentioned material andprovided with the color filter is prepared. Then the substrate 11 andthe sealing substrate 21 are bonded together with the adhesive layer 30in between. In this manner, the display unit as shown in FIG. 7 is thuscompleted.

In the display unit, when a given voltage is applied across the firstelectrode 13 and the second electrode 16, current passes through thelight emitting layer of the organic layer 15 to induce the recombinationof holes and electrons, thereby light emission occurs. This lighttransmits the second electrode 16, the protective film 17 and thesealing substrate 21 and is extracted. Here, the source signal line Y1is divided into the main portion 170 and the crossing portion 160, andin the crossing portion 160, the first layer 161 made of a lowresistance metal and the second layer 162 made of a material having ahigher melting point than that of the first layer 161 are in directcontact with each other so as to reduce the resistance of the crossingportion 160. This realizes a smaller wiring resistance of the sourcesignal line Y1, thereby suppressing a distortion of signal waveform andtransmission delay of signals, etc., to improve the image quality.

As mentioned above, in the display unit of the present embodiment, sincethe source signal line Y1 is divided into the crossing portion 160 andthe main portion 170, and in the crossing portion 160, the first layer161 is in direct contact with the second layer 162 made of a materialhaving a higher melting point than the first layer 161, the resistanceof the crossing portion 160 is lowered. This allows the source signalline Y1 to reduce the wiring resistance, thereby suppressing adistortion of signal waveform and transmission delay of signals and soon, to improve the display quality. In addition, in the display unit ofthe present embodiment, since the first layer 161 and the second layer162 is formed sequentially, the process of manufacturing the displayunit of the present embodiment is simplified. In particular, it issuitably applied to organic electro luminescence displays, in whichlight-emitting performance is susceptible to the fluctuation in theamount of current flow caused by the threshold shift in the drivetransistor Tr1.

Second Embodiment

FIG. 10 is a cross-sectional configuration of a crossing portion 160constituting a source signal line Y1 provided in a display unitaccording to a second embodiment of the present invention. The presentembodiment is the same as that of the first embodiment except for addinga third layer 163 between an insulating substrate 11 and a first layer161 so that the crossing portion 160 may become a three-layer structure.Thus, hereinbelow, component elements corresponding to those in thefirst embodiment are denoted by the same reference numerals.

The third layer 163 is provided to cover the undersurface of the firstlayer 161, which is made of a low resistance metal, so that the firstlayer 161 is reliably protected from a thermal damage given by the laserirradiation heating and pressure resistance of the gate insulating film152 is further improved. Therefore, the third layer 163 is made of amaterial having a higher melting point than the first layer 161. Morespecifically, examples of a component material constituting the thirdlayer 163 include a metal or alloy containing at least one selected fromthe group consisting of molybdenum (Mo), chromium (Cr), titanium (Ti),tungsten (W), tantalum (Ta) vanadium (V), niobium (Nb), nickel (Ni) andmagnesium (Mg) Otherwise, the third layer 163 may be made of a compoundconductive material such as indium oxide or zinc oxide. It is preferredthat the third layer 163 is formed to the thickness of 10 nm to 200 nmfor example because it is preferred for fabrication convenience that thesecond layer 162, the first layer 161 and the third layer 163 are etchedcollectively so that their cross sections may be forward tapered inshape. The third layer 163 may be a single layer or a stacked structureincluding two or more layers.

It is to be noted that, in the present embodiment, among the first tothird layers 161 to 163 constituting the crossing portion 160, it isenough if at least the first layer 161 and the second layer 162 are indirect contact with each other. This is because the third layer 163exerts no direct influence on the wiring resistance since the mainportion 170 of the source signal line Y1 is connected to the secondlayer 162 via the cap layer 164. It is also desirable that the thirdlayer 163 is separated from the first layer 161 by a natural oxidationfilm to avoid a direct contact to each other. This is because it isdesirable that a direct contact between layers is avoided via a naturaloxidation film as far as they do not affect resistance, and the thirdlayer 163 is a portion hardly exerting influence on the wiringresistance. However, since continuous film formation is more simple inmanufacturing, the third layer 163 may be continuously formed on thefirst layer 161 in direct contact therewith.

The display unit may be manufactured in a manner similar to the firstembodiment except that the third layer 163 of the above-mentionedthickness and material, the first layer 161 and the second layer 162 arestacked in order from the insulating substrate 11 side upon formation ofthe crossing portion 160. In this case, the third layer 163, the firstlayer 161 and the second layer 162 may be continuously formed, or onlythe first layer 161 and the second layer 162 may be continuously formed.

Third Embodiment

FIG. 11 shows an example of the cross-sectional configuration when thepresent invention is applied to a liquid crystal display. The presentembodiment is completely the same as the above-mentioned first andsecond embodiments except that the display element is constituted from aliquid crystal display element, and its operation and effects are alsothe same. Thus, component elements corresponding to those in the firstand the second embodiments are denoted by the same reference numerals indescription.

Although configuration of the liquid crystal display element is notlimited in particular, here, as shown in FIG. 11, TFT is formed on theinsulating substrate 11 corresponding to each pixel, and a planarizationinsulating film 42 and a pixel element electrode 43 made of ITO(indium-tin oxide) are formed thereon for example. A common electrode 45which is made of ITO and is formed on an opposing substrate 44 made ofglass etc. is arranged to face the pixel element electrode 43, with aliquid crystal layer 46 in between. Polarizing plates 47 are formed onthe substrate 11 and the opposing substrate 44, respectively so thattheir optical axes (not shown) are orthogonal to each other. It is to benoted that other TFTs, capacitive elements, wiring and so on areprovided on the insulating substrate 11 though not illustrated.

MODULE AND APPLICATION EXAMPLE

Application examples for the display unit according to theabove-mentioned embodiments will be described hereinbelow. The displayunit of the above-mentioned embodiments is applicable to a display ofelectronic equipments in any field, such as TV apparatus, digitalcamera, laptop personal computer, personal digital assistant deviceincluding a portable telephone and video camera, as far as they displaya video signal that is inputted from outside or generated inside as animage or video.

Module

The display unit of the above-mentioned embodiments is built in avarious types of electronic equipments as shown in the after-mentionedapplication examples 1 to 5, as a module as shown in FIG. 12. The moduleis typically configured in such a manner that an exposed region 210 isprovided on one side of a substrate 11 in such a manner as being exposedfrom sealing substrate 21 and adhesive layer 30 so that wirings of asignal line driving circuit 120 and a scanning line driving circuit 130may be extending toward the exposed region 210 to form an externalconnection terminal (not shown) thereon. The external connectionterminal may include a flexible printed circuit (FPC) 220 forinputting/outputting signals.

Application Example 1

FIG. 13 shows an external appearance of a TV apparatus to which thedisplay unit of the above-mentioned embodiments is applied. The TVapparatus includes an image display screen 300 which includes a frontpanel 310 and a filter glass 320, for example, and the image displayscreen 300 is constituted from the display unit of the above-mentionedembodiments.

Application Example 2

FIGS. 14A and 14B show external appearance of a digital camera to whichthe display unit of the above-mentioned embodiment is applied. Thedigital camera includes a light-emitting flash portion 410, a displayportion 420, a menu switch 430 and a shutter button 440 for example, andthe display portion 420 is constituted from the display unit of theabove-mentioned embodiments.

Application Example 3

FIG. 15 shows an external appearance of a laptop personal computer towhich the display unit of the above-mentioned embodiments is applied.The laptop personal computer includes a body 510, a keyboard 520 forinputting characters etc., and a display portion 530 which displays animage for example, and the display portion 530 is constituted from thedisplay unit of the above-mentioned embodiments.

Application Example 4

FIG. 16 shows an external appearance of a video camera to which thedisplay unit of the above-mentioned embodiments is applied. The videocamera includes a body portion 610, a lens 620 which is installed on thefront face of the body portion 610 for shooting objects, a start/stopswitch 630 to be operated when shooting, and a display portion 640, forexample. The display portion 640 is constituted form the display unit ofthe above-mentioned embodiments.

Application Example 5

FIGS. 17A to 17G show external appearance of a portable telephone towhich the display unit of the above-mentioned embodiments is applied.The portable telephone is configured in such a manner that an upperhousing 710 and a lower housing 720 are connected with a connectionpoint (hinge portion) 730, and includes a display 740, a sub display750, a picture light 760 and a camera 770, for example. The display 740or the sub display 750 is constituted from the display unit of theabove-mentioned embodiments.

EXAMPLES

Further, detailed examples of the present invention will be explainedhereinbelow.

Example 1

The pixel driving circuit 140 was formed in a manner similar to theabove-mentioned first embodiment. First, the first layer 161, which wasmade of an Al—Nd alloy to the thickness of 300 nm, and the second layer162, which was made of molybdenum (Mo) to the thickness of 50 nm, werecontinuously formed by a sputtering process on the insulating substrate11 made of glass, without being exposed to the atmosphere. Then, theywere formed into a predetermined shape by photolithography and etchingto obtain the crossing portion 160 (refer to FIG. 8A).

Subsequently, the cap layer 164 which was made of molybdenum (Mo) wasformed by a sputtering process, then formed into a predetermined shapeby photolithography and etching so as to cover the upper surface andside faces of the crossing portion 160. Simultaneously, the gateelectrode 151 was formed with the same material as the cap layer 164(refer to FIG. 8B).

Subsequently, the gate insulating film 152 and the semiconductor film153 were formed by plasma CVD. The gate insulating film 152 had astacked structure including a SiNx layer 152A (100 nm thick) and a SiOxlayer 152B (200 nm thick). The semiconductor film 153 was made ofamorphous silicone (a-Si) and formed to the thickness of 30 nm.

After that, the semiconductor film 153 was irradiated with the laserbeam LB (annealing) using a solid state laser oscillator so as tocrystallize a-Si constituting the semiconductor film 153. At this time,when the laser beam LB scanning along the minor axial direction ofpixels, the lengthwise dimension of the laser beam LB was made a littlenarrower than that of the pixel size as shown in FIG. 4 so that thelaser beam LB is irradiated to the irradiation area defined by theshaded area as shown in FIG. 9, avoiding the crossing portion 160.

After irradiating the semiconductor film 153 with the laser beam LB, theetching stop layer 154 which was made of SiNx to the thickness of 200 nmwas formed on the crystallized semiconductor film 153, and was formedinto a predetermined shape by an etching process so that the etchingstop layer 154 was left only in an area which would finally become thechannel region.

After forming the etching stop layer 154, the n⁺a-Si layer 155 wasformed to the thickness of 100 nm by a CVD process on the etching stoplayer 154 and the crystallized semiconductor film 153, and was formedinto a predetermined shape by an etching process.

After forming the n⁺a-Si layer 155, the source/drain electrode 156,which was formed by stacking an aluminum (Al) layer and a titanium (Ti)layer by a sputtering method, were formed thereon and then formed into apredetermined shape by an etching process. At the same time, the gatewiring X1, the current supply line Y2, and the main portion 170 of thesource signal line Y1 were also formed similarly by stacking an aluminum(Al) layer and a titanium (Ti) layer, and were connected to thesource/drain electrode 156. The main portion 170 of the source signalline Y1 was connected to the crossing portion 160 via the conductiveconnection 180, which was provided in the gate insulating film 152.Further, the passivation film 157 was formed to cover the whole surface.In this manner as mentioned above, the pixel driving circuit 140 shownin FIGS. 1 to 6 was fabricated.

Example 2

The pixel driving circuit 140 was formed in a manner similar to theabove-mentioned Example 1 except for having made the crossing portion160 a three-layer structure as with the above-mentioned secondembodiment. At that time, the third layer 163 was made of molybdenum(Mo) to the thickness of 50 nm. The first layer 161 and the second layer162 were continuously formed without being exposed to the atmosphere.

Comparative Example 1

A pixel driving circuit was formed in a manner similar to theabove-mentioned Example 1 except that a first layer was once exposed tothe atmosphere after formation then a second layer was formed a severalhours later.

Comparative Example 2

A pixel driving circuit, in which wiring was not divided as shown inFIG. 18, was formed. First, a whole source signal line Y1 was formed onan insulating substrate 811. As viewed in its cross-section, the sourcesignal line Y1 was structured as a stacked structure made of a firstlayer and a second layer as with the crossing portion 160 of Example 1.However, the first and second layers were not formed continuously. Morespecifically, after forming a first layer 861 made of an Al—Nd alloy tothe thickness of 300 nm by a sputtering method, it was exposed to theatmosphere. Several hours later, a second layer 862 made of molybdenum(Mo) to the thickness of 50 nm was formed, then they were formed into apredetermined shape by photolithography and etching.

Subsequently, a drive transistor Tr1 and the like were formed in amanner similar to Example 1 except that the laser irradiation to thesemiconductor film was not performed. A gate wiring X1 and a currentsupply line Y2 having a stacked structure of an aluminum (Al) layer anda titanium (Ti) layer were formed when source/drain electrode wasformed, then they were connected to the source/drain electrode.

Evaluation of Wiring Resistance

Measurement of wiring resistance was conducted for the respective sourcesignal lines obtained in Examples 1 and 2 and Comparative examples 1 and2 across both ends of the respective wirings (300 mm in length and 5 μmin width). A lead section of a stacked structure including an aluminum(Al) layer and a titanium (Ti) layer was formed at both ends of therespective wirings of the measurement points so that a contact terminalfor measurement was in contact with the lead section for measurement.The results are shown in Table 1.

TABLE 1 Continuous Formation (direct Source contact) Wiring signal firstSecond Third of 1^(st)/2^(nd) resistance line layer layer layer layersLaser (KΩ) Example 1 divided Al—Nd Mo — conducted irradiated 10 Example2 divided Al—Nd Mo Mo conducted irradiated 10 Comparative divided Al—NdMo — Not irradiated 60 Example 1 conducted Comparative No Al—Nd Mo — NotNot 10 Example 2 divided conducted irradiated

As shown in Table 1, as for Examples 1 and 2 in which the crossingportion 160 was formed by continuously forming the first layer 161 andthe second layer 162, the wiring resistance was equal to the resistanceof Al—Nd alloy, which was the component material of the first layer 161.On the other hand, as for Comparative example 1 in which the first layerand the second layer were not continuously formed, the wiring resistancewas equal to the resistance of molybdenum (Mo), which was the componentmaterial of the second layer 162. It is to be noted that in the case ofComparative example 2, the wiring resistance was suppressed to the levelsame as the resistance of Al—Nd alloy even though the first layer andthe second layer was not formed continuously. That may be because it waspossible for the source signal line Y1, in which its entire wiring had astack structure of the first and second layers without divided wiring,to ignore the influence of resistance components such as surface oxidefilm and so on, since the first and second layers were connected bypinhole or the like at several points. Further, that may be because thefirst layer was not subject to thermal damage by the irradiation heatsince no laser irradiation was conducted, or the like.

Namely, it was fond out that when the source signal line Y1 was dividedinto the crossing portion 160 and the main portion 170, and the crossingportion 160 was constituted in such a manner as continuously forming thefirst layer 161 and the second layer 162 made of a material having ahigher melting point than the first layer 161 so that both layers werein direct contact with each other, the resistance of the crossingportion 160 was lowered so that the wiring resistance in the sourcesignal line Y1 was reduced.

Pressure Proof Evaluation

Pressure proof evaluation was conducted on Examples 1 and 2 andComparative example 2. The first and second layers were formed forExample 1 and Comparative example 2, and the first to third layers wereformed for Example 2 on the whole surface of the insulating substrate11, respectively so that the respective layers were formed into apattern of 30 μm×3500 μm in dimension. Then, each pattern was thoroughlycovered with a cap layer made of molybdenum (Mo). A counter electrodehaving a stacked structure of an aluminum (Al) layer and a titanium (Ti)layer was formed on the respective patterns, with an insulating filmhaving a stacked structure of a SiN layer (300 nm thick) and a SiO₂layer (300 nm thick) in between.

Voltage was applied across the patterns obtained in Examples 1 and 2 andComparative example 2, respectively, and the counter electrode. If oneof the patterns passed a current of 10 to 7 A or more, it was regardedas failure. Cumulative failure rate was thus computed. The results areshown in FIG. 19.

As shown in FIG. 19, a remarkable reduction of failure rate was observedin the case of Example 2 in which the crossing portion 160 was athree-layer structure including the third layer 163 added between theinsulating substrate 11 and the first layer 161. Namely, it was foundout that pressure resistance was able to improve more by providing thethird layer 163 made of a material having a higher melting point thanthe first layer 161 between the insulating substrate 11 and the firstlayer 161.

As mentioned above, although the present invention has been describedwith reference to the foregoing embodiments and examples, the presentinvention is not limited to those but may be variously modified. Forexample, in the above-mentioned embodiments and examples, althoughdescription is made for the case where the source signal line Y1 isdivided for each pixel, it is also possible to design the pixelconfiguration in such a manner that neighboring pixels areline-symmetrical to each other and have a common crystallization areatwo by two so that irradiation of the laser beam LB for crystallizationmay be conducted simultaneously for each pair of the neighboringline-symmetrical pixels two by two. Even in this case, effects similarto the first and second embodiments may be obtained when the crossingportion 160 is disposed outside the irradiation area R of the laser beamLB.

Alternatively, in the above-mentioned embodiments and examples, althoughdescription is made for the case where only the crossing portion 160 ofthe source signal line Y1 has a two-layer structure including the firstand second layers 161 and 162, or a three-layer structure including thefirst to third layers 161 to 163 for example, it is also possible tomake both of the crossing portion 160 and the main portion 170 have thetwo-layer structure or the three-layer structure.

Further, in the above-mentioned embodiments and examples, althoughdescription is made for the case where the source signal line Y1 isdivided into the crossing portion 160 and the main portion 170 forexample, it is also possible to divide the gate wiring X1 and thecurrent supply line Y2.

In addition, for example, the component material and thickness of eachlayer, or the method and condition for forming layers and so on are notlimited to those explained in the above-mentioned embodiments andexamples but other materials, thickness, methods and conditions may beemployed.

Although specific example is given to explain the configuration of theorganic light emitting elements 10R, 10B and 10G in the above-mentionedembodiments, it is not necessary to prepare the all layers, or anotherlayer may be further added.

The present invention is also applicable to a display unit which employsother display elements, such as an inorganic electroluminescent element,electrodeposition/electrochromic display element and so on besides theorganic light emitting element and liquid crystal display element.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. A display unit comprising: an insulating substrate; a plurality of wirings formed to extend in different directions on the insulating substrate; a thin-film transistor; and a display element, wherein, at least one of the plurality of wirings is a divided wiring having a crossing portion formed at an intersection with the other of the plurality of wirings, and a main portion which is formed in a layer same as the other of the plurality of wirings with an insulating film in between and which is electrically connected to the crossing portion via an conductive connection provided in the insulating film, at least one of the main portion and the crossing portion includes a first layer and a second layer stacked in order from the insulating substrate side, the second layer being in direct contact with the first layer and made of a material of a higher melting point than the first layer, and the first layer and the second layer are formed continuously on the insulating substrate.
 2. The display unit according to claim 1, wherein the first layer is made of a metal or an alloy containing at least one selected from the group consisting of aluminum (Al), copper (Cu) and silver (Ag), and the second layer is made of a metal or an alloy containing at least one selected from the group consisting of molybdenum (Mo), chromium (Cr), titanium (Ti), tungsten (W), tantalum (Ta), vanadium (V), niobium (Nb), nickel (Ni) and magnesium (Mg).
 3. The display unit according to claim 1, wherein at least one of the main portion and the crossing portion includes a third layer which is made of a material of a higher melting point than the first layer and is disposed between the insulating substrate and the first layer.
 4. The display unit according to claim 3, wherein the third layer is made of a metal or an alloy containing at least one selected from the group consisting of molybdenum (Mo), chromium (Cr), titanium (Ti), tungsten (W), tantalum (Ta), vanadium (V), niobium (Nb), nickel (Ni), and magnesium (Mg).
 5. The display unit according to claim 1, wherein an upper surface and a side face of the crossing portion are covered with a cap layer made of a material of a higher melting point than the first layer.
 6. The display unit according to claim 1, wherein the plurality of wirings include a source signal line and a gate wiring, the source signal line being the divided wiring.
 7. The display unit according to claim 6, wherein the thin film transistor is formed by annealing a semiconductor film with an irradiation of laser beam, and the crossing portion of the source signal line is formed so as to be located outside an irradiation area of the laser beam.
 8. A method of manufacturing a display unit which is constituted from steps of forming, on an insulating substrate, a plurality of wirings including a source signal line and a gate wiring, a thin film transistor and a display element, wherein the step of forming the plurality of wiring comprising the steps of: forming a crossing portion of the source signal line at an intersection with the gate wiring; forming an insulating film on the insulating substrate on which the crossing portion is formed; and forming a main portion of the source signal line and the gate wiring on the insulating film and providing a conductive connection in the insulating film for electrically connecting the main portion and the crossing portion, and in the step of forming the crossing portion of the source signal line, a first layer and a second layer made of a material of a higher melting point than the first layer are continuously formed in order from the insulating substrate side.
 9. The method of manufacturing the display unit according to claim 8, wherein the first layer is made of a metal or an alloy containing at least one selected from the group consisting of aluminum (Al), copper (Cu) and silver (Ag), and the second layer is made of a metal or an alloy containing at least one selected from the group consisting of molybdenum (Mo), chromium (Cr), titanium (Ti), tungsten (W), tantalum (Ta), vanadium (V), niobium (Nb), nickel (Ni), and magnesium (Mg).
 10. The method of manufacturing the display unit according to claim 8, wherein, in the step of forming the crossing portion of the source signal line, a third layer made of a material of a higher a melting point than the first layer, the first layer and the second layer are continuously formed in order from the insulating substrate side.
 11. The method of manufacturing the display unit according to claim 10, wherein the third layer is made of a metal or an alloy containing at least one selected from the group consisting of molybdenum (Mo), chromium (Cr), titanium (Ti), tungsten (W), tantalum (Ta), vanadium (V), niobium (Nb), nickel (Ni) and magnesium (Mg).
 12. The method of manufacturing the display unit according to claim 8, wherein an upper surface and a side face of the crossing portion are covered with a cap layer made of a material of a higher melting point than the first layer.
 13. The method of manufacturing the display unit according to claim 12, wherein a gate electrode of the thin film transistor is formed with the same material as the cap layer, simultaneously with the formation of the cap layer.
 14. The method of manufacturing the display unit according to claim 8, wherein the step of forming the thin film transistor includes a step of annealing a semiconductor film with an irradiation of laser beam, and the crossing portion of the source signal line is formed to be located outside an irradiation area of the laser beam. 